Single wire battery pack temperature and identification method

ABSTRACT

Disclosed are techniques for identifying battery pack types and by inference battery chemistries by measuring a transient response of the battery pack to signal applied to the battery pack.

BACKGROUND

Conventional chargers rely on an electrical, mechanical or digitalsignal technique to determine the type of battery being charged and thusthe appropriate charge regime to apply. For example, some techniques arebased on the use of an internal battery ID resistor, the value of whichdetermines the charging parameters applied for that specific battery.Mechanical techniques have also been used, such as using the location ofa connector polarity key or the location of a particular connector pinto distinguish between different battery models requiring differentcharging parameters. The Smart Battery SMBus standards, for example, usea serial data communications interface to communicate the chargingparameters to the charging device. The above approaches require addedconnection points beyond the battery power terminals or some addedmechanical feature not required for the basic battery function ofdelivering stored energy to a portable device. In the case of the SmartBattery standards, for example the SMBus standard, an electrical circuitand at least two additional connector pins are required to implement thesmart interface between the charger and battery, adding to the cost,complexity and size of the battery.

SUMMARY

Thus, for cost sensitive applications such conventional techniques haveconcomitant disadvantages.

In one aspect, a method for identifying a type of battery pack includesapplying a signal to a sense terminal of the battery pack, measuring atransient response of the battery pack to the applied signal anddetermining from the measured transient response the battery pack type.

Embodiments may include one or more of the following.

The method includes determining a charging current to be applied to thebattery based on the measured transient response and applying thedetermined charging current to the battery. The method includes applyingthe signal by causing a first terminal of a controller unit of a batterycharger to a low state and measuring the transient response of thebattery to the signal at a second, different terminal of the controllerunit of the battery charger. Measuring the transient response includesmeasuring a voltage between a terminal of the battery pack and an inputto a controller in response to applying the signal at a first timeinstance and measuring the voltage between the terminal of the batterypack, and the input of the controller in response to applying the signalat a subsequent time instance. Measuring the transient response includescomputing a value of the transient response over the first andsubsequent instances of time. Determining the battery pack type includesaccessing a lookup table storing transient response values, associatedwith plural, different battery packs to provide an indication of batterypack type. The battery is lithium-iron-phosphate electrochemical cell.

The method further includes accessing a lookup table storing multiplecharging current values, associated with a corresponding identifiedbattery type, periodically measuring the voltage between terminals ofthe battery, and adjusting the charging current applied to the batterywhen the measured voltage between the terminals of the battery reaches apre-determined voltage value such that the voltage between the terminalsof the battery is maintained at the pre-determined voltage value. Thebattery pack comprises a resistor and the transient response of thebattery pack is measured taking into consideration the value ofresistance of the resistor. The resistor is a thermistor and thetransient response of the battery pack is measured taking intoconsideration the value of resistance of the thermistor. The methodfurther includes measuring the value of resistance of the thermistor toinfer a value of temperature of the battery in the battery pack.

According to an additional aspect of the present invention, a chargingdevice is configured to charge a rechargeable battery housed in abattery pack. The battery pack includes at least one rechargeableelectrochemical cell, the charging device comprising a chargingcompartment configured to receive the battery, the charging compartmenthaving electrical contacts configured to be coupled to respectiveterminals of the battery; and a controller configured to apply a signalto a terminal of the battery pack, measure a transient response of thebattery pack to the applied signal and determining the battery pack fromthe measured transient response.

Embodiments may include one or more of the following.

The controller is further configured to cause the determined chargingcurrent to be applied to the battery. The device further includes acapacitor coupled to a first input of the controller and a resistorcoupled to an output terminal of the controller, the output terminalsupplying the signal to the battery pack. The controller is configuredto determine the transient response of the battery pack to the signalby:τ_(BP1) =R _(th) ∥R _(pd) ∥R _(pu)×(C _(—a/d))where R_(th) is a resistor in the battery pack R_(pd) and R_(pu) areresistors coupled to the output terminal and a voltage supply of thecontroller, respectively, and C_(—a/d) is the capacitor coupled to thefirst input of the controller.

The controller is configured to determine the transient response of thebattery pack to the signal by:τ_(BP2) =R _(th) ∥R _(pd) ∥R _(pu)×(C _(—a/d) +C _(—bp2))where R_(th) is a resistor in the battery pack R_(pd) and R_(pu) areresistors coupled to the output terminal and a voltage supply of thecontroller, respectively, C_(—a/d) is a capacitor coupled to the firstinput of the controller and C_(—bp2) is a capacitor coupled to aterminal of the battery pack in parallel with the resistor R_(th).

The rechargeable battery includes a lithium-iron-phosphate rechargeablecell.

A battery pack for housing a rechargeable battery, includes a housing, aresistor disposed in the housing of the battery pack, the resistorhaving one end coupled to a reference terminal and second end coupled toa sense terminal of the battery pack, and a capacitor coupled to theterminal of the battery pack and the reference terminal in parallel withthe resistor.

Embodiments may include one or more of the following.

The battery pack includes a positive output terminal that is configuredto couple to an anode of a rechargeable battery. The battery packincludes a rechargeable cell disposed in the battery pack having ananode terminal coupled to the positive output terminal of the batterypack and a cathode coupled to the reference terminal of the batterypack. The battery output terminal of the battery pack and the senseterminal of the battery pack are different terminals, with the batteryoutput terminal electrically isolated from the sense terminal.

One or more of the above aspects may include one or more of thefollowing advantages.

The above arrangements may accurately determine the type of batterychemistry present, and thus deliver the appropriate charging regime forthe battery that is present. These arrangements also permit the chargersto be used for charging different types of batteries or battery packs,while also being able to accurately monitor the temperature of thebatteries or battery pack. Other advantages include elimination ofexpensive microprocessors, microcontrollers, or controllers in thebattery pack, and elimination of an extra pin since battery temperatureand battery/battery pack type can be ascertained from signals on acommon pin. With the above arrangements, the accuracy in the measurementof a thermistor resistance value is unaffected when identifying batterytypes.

Other features and advantages of the invention will be apparent from thedescription and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary charger system.

FIGS. 2 and 3 are diagrams depicting circuits for identifying battery orbattery pack type for use in a charger such as that shown in FIG. 1.

FIGS. 4-7 are flow diagrams of exemplary charger routines.

FIGS. 8-11 are plots of voltage vs. time.

DETAILED DESCRIPTION

System Description

Described is a technique for inexpensively differentiating betweenbattery chemistries/battery pack types on a universal charger system, aswell as monitoring temperature of the battery pack over a single sharedelectrical connection. Such a charger is configured to determine, applyand control charging current for charging a rechargeable battery withoutthe need for prior knowledge of the battery type and/or capacity. Thecharger is not limited to, but is particularly useful for chargingbattery cells of various sizes, including battery cells used in manymodern portable consumer electronic products, such as cellulartelephones, MP3 players and digital cameras. The disclosed charger maybe applied to many different rechargeable battery types, includinglithium ion batteries having high rate charge capability, such as thoseusing lithium iron-phosphate or similar phosphate based intercalationcompounds as one of the battery electrodes, as well as lithium-ionbatteries, and also lead-acid, nickel metal hydride, nickel cadmium,nickel zinc, and silver zinc batteries. The disclosed charger mayfurther be configured to charge different types of batteries, including,for example, cylindrical batteries, prismatic batteries, button-cellbatteries, and so forth.

Referring to FIG. 1, an adaptive charger 10 configured to chargebatteries in a battery pack and to determine a transient response of thebattery pack in order to identify the battery pack type is shown. Thebattery pack includes one or more batteries 12 having one or moreelectrochemical cells that is received in a receptacle or compartment(not shown) of the charger 10. The battery 12 is a secondary cell. Whileprimary electrochemical cells are meant to be discharged, e.g., toexhaustion, only once, and then discarded secondary cells are intendedto be recharged. Primary cells are described, for example, in DavidLinden, Handbook of Batteries (McGraw-Hill, 2d ed. 1995). Secondaryelectrochemical cells can be recharged for many times, e.g., more thanfifty times, a hundred times, or more times. Secondary cells aredescribed, e.g., in Falk & Salkind, “Alkaline Storage Batteries”, JohnWiley & Sons, Inc. 1969; U.S. Pat. No. 345,124; and French Patent No.164,681, all hereby incorporated by reference. In the embodimentsdescribed herein, the battery 12 is a secondary, or rechargeable,battery.

The charger 10 is coupled to a power conversion module 11. The powerconversion module 11 includes an AC-DC power converter 13 thatelectrically couples to an external AC power source, such as a sourceproviding power at a rating of 96V-220V and 50 Hz-60 Hz, and convertsthe externally supplied AC power to a DC power level suitable forcharging rechargeable batteries (e.g., DC power levels of approximatelybetween 3.8-4.2 V). The AC-DC power converter 13 may be implemented asan AC-DC switcher configured to accept input power at a first voltageand transform it to a lower voltage.

In some embodiments, a DC-DC power converter 15 is incorporated into thepower conversion module 11 that is adapted to convert an external DCpower source, such as a car's DC power supply, to a DC power levelsuitable for charging rechargeable batteries may be used. Other powerconversion configurations may also be used.

The charger 10 determines a charging current to be applied to therechargeable battery 12 based on a measured transient response of thebattery pack 12 incorporating the batteries. The value of the measuredtransient response is indicative of the battery pack type that is beingcharged by the charger 10, and thus enables a controller 14 to determinethe charging current level to apply to the battery 12. Varioustechniques could be used for determining the charging current regime toapply such as by using a look up table that is indexed by valuesdetermined for the transient response of the battery, as discussed belowto determine the charge regime.

The measured transient response is used as identification mechanism toidentify the particular battery pack type (and from which can beinferred battery chemistry of the battery 12 in the battery pack). Themeasured transient response is of a resistor typically, a thermistorcoupled to the battery pack and an added capacitance (FIG. 3). In suchembodiments, the charger 10 identifies the battery pack by measuring thetransient response of the resistance of the thermistor and capacitanceof the battery pack, as will be discussed below.

The controller 14 is configured to control the operation of the charger10, including measuring the transient response that is used to identifythe type of battery pack connected to the charger 10, and to determinethe charging current and/or charging profile (e.g., duration of chargingperiod, adjustment of charging current and/or voltage at certain timeinstances, etc.) to apply to the battery 12. Various resistance valuesof thermistors (or resistors) are used in combination with astandardized measurement scheme to identify different battery pack types(FIG. 2). In an alternative, various resistance values of thermistors(or resistors) in combination capacitance values of added capacitors inthe battery pack are used in combination with a standardized measurementscheme to identify the different battery pack types (FIG. 3).

The controller 14 includes a processor device 16 configured to controlthe charging operations performed on the battery 12 and controloperations, as will be described below. The processor device (MCU) 16may be any type of computing and/or processing device, such as aPIC18F1320 microcontroller from Microchip Technology Inc. The processordevice 16 used to implement the charger 10 can include volatile and/ornon-volatile memory elements configured to store software containingcomputer instructions to enable general operations of theprocessor-based device, as well as implementation programs to performcharging operations on the battery 12 connected to the charger, based onthe at least one measured electric characteristic of the rechargeablebattery 12.

In this example, the processor 16 includes an analog-to-digitalconverter (ADC) 20 that receives signals from transient voltage sensecircuits 27 (described below) indicative of the battery pack. From theindication of battery pack type a suitable charging regime is selected.

The controller 14 further includes a digital-to-analog converter device(DAC), 22, and/or a pulse-width modulator (PWM), 24, that receivesdigital signals generated by the processor device 16, and generates inresponse electrical signals that regulate switching circuitry, such as aDC/DC converter 26, e.g., a buck type converter.

Referring now to FIG. 2, a first exemplary charger system 40 includesthe MCU 16 and voltage sense circuit 27 comprised of resistors R_(pd)and R_(pu), capacitor C_(a/d) and a Battery Pack 1. The charger system40 is configured to supply charging current to the Battery Pack 1. TheMCU determines the transient response to a signal from resistors R_(pd)and R_(pu), capacitor C_(a/d) and the thermistor in Battery Pack 1, asdiscussed below. The thermistor in Battery Pack 1 is a temperaturesensing circuit element, R_(th), as otherwise commonly available inbattery packs to measure temperature of the battery pack. Battery 12(FIG. 1) is shown in the battery pack BP_1 with the battery pack havinga housing 29.

Identifying the battery pack (and inferring battery chemistry and/orbattery configuration) is based on the host Micro Controller Unit (MCU)measuring transient voltage response to a signal passed through thepassive circuit components (R_(pd) and R_(pu), capacitor C_(a/d) and thethermistor R_(th)). The A/D (Analog to Digital Converter) has an inputto which the resistors R_(pd) and R_(pu), and capacitor C_(a/d) have oneend coupled. The MCU through the A/D input monitors battery packtemperature and identifies the battery pack type. The MCU also includesan I/O pin (input/output). By driving the I/O (input/output) pin high orlow, respectively, over this single shared electrical connection, atransient response is generated from the battery pack and the MCU canmeasure this transient response at the A/D connector pin.

Referring now to FIG. 3, another exemplary system 40′ includes BatteryPack 2. The system includes the sense circuit 27 comprised of resistorsR_(pd) and R_(pu), capacitor C_(a/d) and host MCU (microcontrollerunit). The charger system 40′ is configured to supply charging currentto the Battery Pack 2. The resistors R_(pd) and R_(pu), in combinationwith capacitor C_(a/d) are used to sense the transient voltagecharacteristics of Battery Pack 2, as discussed below. The Battery Pack2 includes a thermistor, (temperature sensing circuit element), R_(th),as in other commonly available battery packs. In this system to furtherdifferentiate between different battery packs Battery Pack 2 includes anadded capacitor C_(bp2) coupled in shunt across the temperature sensingcircuit element, thermistor R_(th). The battery 12 (FIG. 1) is shown inthe battery pack BP_2 the battery pack having a housing 29 a.

Identifying the battery pack (and inferring battery chemistry and/orbattery configuration) is based on the host Micro Controller Unit (MCU)measuring transient voltage response of a signal through the passivecircuit components (resistors R_(pd) and R_(pu), capacitor C_(a/d)thermistor R_(th) and added capacitor C_(bp2)).

As with the system 40 of FIG. 2, the Host charger MCU includes an A/D(Analog to Digital Converter) to which the resistors R_(pd) and R_(pu),capacitor C_(a/d) have one end coupled to. The MCU through the A/D inputpin monitor battery pack temperature and identify the battery pack type.The MCU also includes an I/O pin (input/output). By driving the I/O(input/output) pin high or low, respectively, over this single sharedelectrical connection the MCU can measure the transient response of thesignal at the A/D connector.

The configurations of FIGS. 2 and 3, above provide RC(Resistive-Capacitive) circuit equivalents, and RC time constants,(τBP1) and (τBP2) for Battery Pack 1 and Battery Pack 2, respectively.Also, if there is no battery pack installed, there is a time constant,τSYS for system start up time, and when {S0} is sampled, the system willremain in standby STBY, as seen in Plot 1 (FIG. 8).

Referring to FIG. 4, a main sequence 50 of the MCU is illustrated. Uponcharger power on, 51, the charger waits 52 for a predetermined period oftime, e.g., 100 ms and goes into a standby 53 mode. After a battery packinstallation is detected the battery voltage is sampled 54 S₀ at the A/Dconverter input (See plot of FIG. 8). Depending on the value of S₀, 55a, 55 b, the sequence either issues an error 56, goes back to standby54, via a wait 57 or invokes the ID_THERM routine 60.

Referring now to FIG. 5, the ID_THERM routine 60 is shown. After abattery pack installation is detected and the voltage on the thermistorpin of the battery pack stabilizes (after approximately 1 second) 62,(as illustrated in FIG. 9 or 10 (Plot 2A and Plot 2B)), battery packtemperature is verified, by S₀ being outside a hot 64 or cold 66 rangeand if the value of S₀ is above 4.5 V (indicating that the battery isnot present), the charger returns to standby 68 otherwise the chargerinvokes the ID Select procedure 70 to determine the time constant (τ)provided by the battery pack and charger circuitry combination.

Referring now to FIG. 6, a time constant for the battery pack ismeasured 70 by applying a waveform to the thermistor (Battery Pack 1) orthrough the thermistor/capacitor combination (Battery Pack 2) by causing72 I/O pin on the MCU to go to a low level. When the I/O pin isconnected to the thermistor with via the resistor, R_(pd), and forced tolow level, the capacitors C_(bp2) and/or C_(a/d) begin to discharge. Theprocess waits 74 (e.g., for 15 ms) and the signal at the thermistor issampled {S1} 76 (plot 3, FIG. 11) and later, after waiting 78 for thevoltage to stabilize (after 300 ms,) is again sampled 80 ({S2}).

Placing a capacitor, C_(bp2), which is much larger than the host A/D pinfilter capacitor, C_(a/d), in parallel with the battery pack thermistor,(Battery Pack 2) provides a much larger time constant (τ_(BP2)) than thetime constant (τ_(BP1)) associated with a pack with solely a thermistor(Battery Pack 1). In the case of Battery Pack 2 being present, {S1} issignificantly greater than {S2}. In the case of Battery Pack 1 beingpresent, {S1} is close to but not equal to {S2}.

Conditional operations performed by the MCU on the sampled signalssubsequently identify the type of battery pack. Conditional operationsinclude comparing S₁ to S₀ to determine if the MCU routine should invoke82 the ID_THERM process (S₁<S₀*0.9) or if the sample S₁ is greater than(S₂*1.1) 84, (S₂ being the quiescent value) forcing the I/O pin high 86,and if the battery voltage is greater than or equal to 2.0V, 88 identify90 as battery pack 2 or if not returning 92 to a pre-charge routine. Ifthe sample S₁ is not greater than (S₂*1.1) 84 the process 70 pulls theI/O pin high 94 and if the battery voltage is not greater than or equalto 2.0V, 97 invokes 96 the pre-charge routine or if the battery voltageis greater than 2.0V identify the battery pack 98 as battery pack 1.

Referring now to FIG. 7, a pre-charge routine 100 starts a timer 102,determines 104 if the battery voltage is greater than 2.2 volts, and ifso invokes 106 the ID₁₃ THERM routine. If the battery voltage is notgreater than 2.2 volts and timer is at 60 seconds, the pre-chargeroutine invokes an error 112, otherwise the routing pre-charges 110 thebattery with a specified current, e.g., 500 ma.

The voltage waveforms for the two different pack types are illustratedin Plot 3 (FIG. 10). After the determination of the battery pack typethe I/O pin is pulled high, and the charger system determines batteryvoltage to either initialize pre-charge, or battery pack specific chargeregime, and temperature is monitored throughout the charge cycle.

Exemplary charging regimes and details on chargers can be found inpublished applications US-2008-023836-A1 or US-2008-0238362-A1 each ofwhich are incorporated herein by reference.

The timing required in taking data samples {S0}, {S1} and {S2} isselected to ensure sufficient resolution between data sample values toaccount for component and power supply tolerances, and variations in theRC time constants throughout the temperature range.

Curves for Plots 1, 2A, 2B, and 3 (FIGS. 8-11) are calculated for thefollowing values:Vcc=4.9VR _(pu)=155 kOhms(+1%)R _(pd)=33.2 kOhms(+1%)C _(—a/d)=0.022 uF(+15%)C _(—bp2)=1 uF(+15%)

Using values with upper % tolerances, the plot curves and calculationsare for maximum RC time constants.

During System Start-up with No Battery pack (FIG. 8):τ_(SYS) =R _(pu) ×C _(—a/d)

During System Power ON with Battery pack installed (FIG. 9):

Battery Pack 1:τ_(BP1) =R _(th) ∥R _(pu) ×C _(—a/d)

Battery Pack 2:τ_(BP2) =R _(th) ∥R _(pu)×(C _(—a/d) +C _(—bp2))

During System Powered ON in STBY, and Battery pack Inserted (FIG. 10):

Battery Pack 1:τ_(BP1) =R _(th) ∥R _(pu) ×C _(—a/dD)

Battery Pack 2:τ_(BP2) =R _(th) ∥R _(pu)×(C _(—a/d) +C _(—bp2))

During ID Select with Battery pack Installed (FIG. 11):

Battery Pack 1:τ_(BP1) =R _(th) ∥R _(pd) ∥R _(pu)×(C _(—a/d))

Battery pack 2:τ_(BP2) =R _(th) ∥R _(pd) ∥R _(pu)×(C _(—a/d) +C _(—bp2))

Based on various values of the transient response, different batterypacks can be identified. From these battery packs different chargeregimes can be used.

As an illustrative example, a look up table can be produced. Exemplaryfields can include:

Transient Battery Number response pack Battery Battery of value typechemistry configuration batteries Value 1 * * * Value n

An identification scheme is provided for battery pack types and byinference, battery chemistries with the foregoing. By assigningdifferent values of transient response, e.g., fall time, to differentbattery pack types and knowing the configuration of the batteries inparticular battery packs a look-up table can be populated and accessedto identify a battery pack type. Other arrangements are possible. Withknowledge of the battery pack type an inference of battery chemistry andnumber of cells, and configuration can be made. Such information can bestored in a look-up table or the like accessible by a controller unitthat is part of a battery charger unit. This information can be directlyor indirectly used to select a particular charging regime for chargingbatteries in the identified battery pack.

Aspects of the invention can be implemented in digital electroniccircuitry or in computer hardware, firmware, software, or combinationsthereof. Apparatus of the invention can be implemented in a computerprogram product tangibly embodied in a machine-readable storage devicefor execution by a programmable processor such as the MCU; and methodactions can be performed by a programmable processor such as the MCUexecuting a program of instructions to perform functions. The inventioncan be implemented advantageously in one or more computer programs thatare executable on a programmable system including at least oneprogrammable processor coupled to receive data and instructions from,and to transmit data and instructions to, a data storage system, atleast one input device, and at least one output device. Each computerprogram can be implemented in a high-level procedural or object orientedprogramming language, or in assembly or machine language if desired; andin any case, the language can be a compiled or interpreted language.Suitable processors include, by way of example, both general and specialpurpose microprocessors. Generally, a processor will receiveinstructions and data from a read-only memory and/or a random accessmemory. Storage devices suitable for tangibly embodying computer programinstructions and data include all forms of non-volatile memory,including by way of example semiconductor memory devices, such as EPROM,EEPROM, and flash memory devices and the like. Any of the foregoing canbe supplemented by, or incorporated in, ASICs (application-specificintegrated circuits) implemented as state machine structures or thelike.

Other Embodiments

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

Alternate embodiments are envisioned. For example, an alternateembodiment would have an inductor disposed in series with thethermistor. A battery pack with an inductor in series with thethermistor has one end of the series combination connected to theID/Therm contact pad, and the other end connected to the commonterminal. When the battery pack is inserted, and Vcc voltage is appliedto the ID/Therm contact pad, current flows through the inductor andthermistor to generate a voltage potential in relation to the directionof current flow. When identifying battery pack chemistry (two batterypacks, Battery Pack 1 consisting of a sole thermistor, and Battery Pack2 including a thermistor in series with an inductor), the voltagepotential through V_(cc) is abruptly disconnected, by circuitry insidethe charger. If Battery Pack 2 is present, current will drop rapidly asa function of time, thus it can be shown from the following equation:v(t)=L×((di/dt)×(t))

where: L=Inductor Value in Henrys

-   -   i=Current in Amps    -   v=Voltage in Volts

When voltage is disconnected abruptly in a short time, for Battery Pack2, di/dt will correspond to a negative change in current over time (t),which will result in a negative voltage across the inductor for thattime (t), as current flows in the opposite direction. If Battery Pack 1is present, the voltage will only drop to zero.

Another alternative embodiment includes measuring the time constantquickly after battery pack insertion or start up, where(C_(—bp2)>>C_(—a/d)) and also knowing that Battery Pack 1 has solely athermistor, and Battery Pack 2 has a thermistor in parallel withC_(—bp2). The process for identifying a battery pack would occur quicklyafter startup with battery pack already installed or quickly after thebattery pack insertion is detected, measuring the time constant uponfirst charging the RC rather than applying a signal to the RC networkseparately. In this approach the I/O pin and R_(pd) are not required,reducing the cost, complexity and the time required to performidentification. Conversely, such a system would require a free interruptin the MCU which can be dedicated solely to being triggered upon batteryinsertion.

The battery packs of FIGS. 2 and 3 have the same thermistor componentR_(th) on both battery packs. The host device contains an MCU with A/Dfunctionality and provides a well regulated V_(cc) power rail. Thecomponent C_BP2 in Battery Pack 2 is chosen to be substantially greaterthan C_(—A/D).

In other embodiments, different battery packs can have differentthermistor values and thus different, albeit less dramatic variations intransient response are provided from the battery packs.

This arrangement provides a charger configured to determine, apply andcontrol charging current for charging a rechargeable battery without theneed for prior knowledge of the battery or battery pack type and/orcapacity.

What is claimed is:
 1. A method comprises: identifying a type of batterypack and a temperature of the battery pack by: receiving by a controllerdevice, an interrupt signal triggered upon: (i) insertion of the batterypack into a charging device or (ii) controller device startup when thebattery pack is already installed in a charging device; measuring by acontroller device, in response to the interrupt signal, a voltage on asense terminal of the battery pack that has a thermistor coupled to thesense terminal; determining by the controller device from the measuredvoltage, the temperature of the battery pack; measuring by thecontroller device a transient response of the battery pack to receivingthe interrupt signal; and determining from the measured transientresponse the battery pack type.
 2. The method of claim 1, furthercomprising: determining a charging current to be applied to the batterybased on the measured transient response; and applying the determinedcharging current to the battery.
 3. The method of claim 1, furthercomprising: applying by the controller device a signal to the senseterminal of the battery pack; measuring by the controller device atransient response of the battery pack to the applied signal applied tothe sense terminal; applying the signal by causing a first terminal of acontroller unit of a battery charger to a low state with the firstterminal of the controller unit being coupled to the sense terminal ofthe battery pack; and measuring the transient response of the battery tothe applied signal at a second, different terminal of the controllerunit of the battery charger.
 4. The method of claim 1, furthercomprising: applying by the controller device a signal to the senseterminal of the battery pack; measuring by the controller device atransient response of the battery pack to the applied signal applied tothe sense terminal; measuring the voltage between the sense terminal ofthe battery pack and an input to a controller in response to applyingthe signal at a first time instance; and measuring the voltage betweenthe sense terminal of the battery pack and the input of the controllerin response to applying the signal at a subsequent time instance.
 5. Themethod of claim 4, further comprising: computing a value of thetransient response over the first and subsequent instances of time. 6.The method of claim 1, wherein determining the battery pack comprises:accessing by the controller device a lookup table storing transientresponse values, associated with plural, different types of batterypacks to provide an indication of battery pack type.
 7. The method ofclaim 1, wherein the battery is lithium-iron-phosphate electrochemicalcell.
 8. The method of claim 1, further comprising: accessing by thecontroller device a lookup table storing transient response values,associated with plural, different types of battery packs to provide anidentification of battery pack type; accessing by the controller devicea second lookup table storing multiple charging current values,associated with the identified battery type; periodically measuring thevoltage between terminals of the battery; and adjusting the chargingcurrent applied to the battery when the measured voltage between theterminals of the battery reaches a pre-determined voltage value suchthat the voltage between the terminals of the battery is maintained atthe pre-determined voltage value.
 9. The method of claim 1 wherein thebattery pack comprises a resistor and the transient response of thebattery pack is measured taking into consideration the value ofresistance of the resistor.
 10. The method of claim 9 wherein theresistor is a thermistor and the method further comprises: measuring bythe controller the value of resistance of the thermistor to infer avalue of temperature of the battery in the battery pack; determining bythe controller, the transient response of the battery pack is measuredtaking into consideration the value of resistance of the thermistor. 11.The method of claim 10, wherein the battery pack further includes acapacitor and an inductor and the method further comprises: determiningby the controller, the transient response of the battery pack takinginto consideration resistance of the thermistor, inductance of theinductor, and capacitance of the capacitor, measuring the value ofresistance of the thermistor to infer a value of temperature of thebattery in the battery pack.
 12. A charging device comprises: a chargingcompartment configured to receive a rechargeable battery housed in abattery pack, the charging compartment having electrical contactsconfigured to be coupled to respective sense, reference and outputterminals of the battery pack; and a controller configured to: receivean interrupt signal triggered upon: (i) insertion of the battery pack or(ii) controller device startup with the battery pack already installed;measure a resistance value at the sense terminal; determine from themeasured resistance the temperature of the battery pack; measure, inresponse to the interrupt signal, a transient response of the batterypack; and determine the battery pack type from the measured transientresponse.
 13. The device of claim 12 wherein the controller is furtherconfigured to: cause the determined charging current to be applied tothe battery.
 14. The device of claim 12 further comprising: thecontroller further configured to: apply a signal to the sense terminalof the battery pack; and measure a transient response of the batterypack to the applied signal that is applied to the sense terminal; acapacitor coupled to a first input of the controller; and a resistorcoupled to an output terminal of the controller, the output terminalsupplying the signal to the battery pack.
 15. The device of claim 14wherein the controller is configured to determine the transient responseof the battery pack to the signal by:τ_(BP1) =R _(th) ∥R _(pd) ∥R _(pu)×(C _(—a/d)) where R_(th) is aresistor in the battery pack, R_(pd) and R_(pu) are resistors coupled tothe output terminal and a voltage supply of the controller respectively,and C_(—a/d) is the capacitor coupled to the first input of thecontroller.
 16. The device of claim 14 wherein the controller isconfigured to determine the transient response of the battery pack tothe signal by:τ_(BP1) =R _(th) ∥R _(pd) ∥R _(pu)×(C _(—a/d) +C _(—bp2)) where R_(th)is a resistor in the battery pack, R_(pd) and R_(pu) are resistorscoupled to the output terminal and a voltage supply of the controllerrespectively, C_(—a/d) is a capacitor coupled to the first input of thecontroller, and C_(—bp2) is a capacitor coupled to a terminal of thebattery pack in parallel with the resistor R_(th).
 17. The device ofclaim 12 further comprising the battery pack, with the rechargeablebattery and with the battery pack further comprising: alithium-iron-phosphate rechargeable battery as the rechargeable battery;the housing having the reference, output and sense terminals; a resistordisposed in the housing, the resistor having one end coupled to thereference terminal and second end coupled to the sense terminal; and acapacitor coupled to the sense and reference terminals in parallel withthe resistor.
 18. A battery pack for housing a rechargeable battery,comprising: a housing having a reference, an output terminal, and asense terminal; a rechargeable battery disposed in the housing, therechargeable battery having a reference terminal coupled to thereference terminal of the housing and an output terminal coupled to theoutput terminal of the housing; a resistor disposed in the housing ofthe battery pack, the resistor having one end coupled to the referenceterminal of the battery pack and second end coupled to the senseterminal of the battery pack; a capacitor coupled to the sense terminalof the battery pack and the reference terminal of the battery pack, andcoupled in parallel with the resistor; and an inductor coupled in serieswith the resistor between the reference terminal of the battery pack andthe sense terminal of the battery pack.
 19. The battery pack of claim 18wherein the output terminal of the battery pack is further comprising: apositive output terminal of the battery pack that is configured tocoupled to the output terminal of the rechargeable battery that is ananode of the rechargeable battery.
 20. The battery pack of claim 19wherein the reference terminal of the battery pack is coupled to acathode of the rechargeable battery further comprising: a rechargeablecell disposed in the battery pack having an anode terminal coupled tothe positive output terminal of the battery pack and a cathode coupledto the reference terminal of the battery.
 21. The battery pack of claim18 wherein the battery output terminal of the battery pack and the senseterminal of the battery pack are different terminals, with the batteryoutput terminal electrically isolated from the sense terminal.
 22. Thebattery pack of claim 18 wherein the resistor is a thermistor that has aresistance characteristic that changes with temperature.
 23. The batterypack of claim 18 wherein the battery pack is identified using at leastone of: (i) the resistance of the thermistor, (ii) the inductance of theinductor, and (iii) the capacitance of the capacitor, and the batterypack temperature is determined using the resistance of the thermistor.24. The battery pack of claim 18 wherein the rechargeable batteryincludes a lithium-iron-phosphate rechargeable battery.
 25. The batterypack of claim 18 wherein the rechargeable battery is one or morelithium-iron-phosphate rechargeable batteries and the resistor is athermistor and the capacitor has a capacitance value of about 1 uf. 26.The battery pack of claim 18 that is configured to be charged by acharger, and wherein the capacitor has a substantially high capacitancevalue in comparison to a capacitance value of an input terminal to thecharger that receives a transient signal from the sense terminal. 27.The method of claim 10, wherein the battery pack further includes acapacitor and an inductor and the method further comprises: determiningby the controller, the transient response of the battery pack takinginto consideration resistance of the thermistor, inductance of theinductor, and capacitance of the capacitor, measuring the value ofresistance of the thermistor to infer a value of temperature of thebattery in the battery pack.
 28. The device of claim 12 furthercomprising the battery pack, with the rechargeable battery and with thebattery pack further comprising: a lithium-iron-phosphate rechargeablebattery as the rechargeable battery; the housing having the reference,output and sense terminals; a resistor disposed in the housing, theresistor having one end coupled to the reference terminal and second endcoupled to the sense terminal; and a capacitor coupled to the sense andreference terminals in parallel with the resistor; an inductor coupledin series with the resistor between the reference terminal and the senseterminal; wherein the controller is configured to determine thetransient response of the battery pack to an abrupt interruption to thevoltage of the signal by measuring a voltage across the inductor.